Telephone sets, i.e., base unit and handset, whether corded, cordless, or speakerphone, typically employ Automatic Gain Control (AGC) or other nonlinear circuits to suppress telephone line noise, static, and/or acoustic feedback. Such circuits are intended to eliminate or reduce noise that would otherwise be heard by a user at the handset speaker during a telephone communication. However, in some designs, such circuits can operate excessively with the result that the user is likely to hear a “choppy” sound quality. That is, the user may find that a far end talker with a quiet voice is difficult or impossible to understand because too many of the talker's syllables are suppressed or cutoff, resulting in the “choppy” sound.
Additionally potential sources of poor telephone sound quality include:                Signal overload with resulting distortion        Signal underload with resulting noise        Insufficient digital quantization resolution and/or range        Low digital sampling rate        Excessive low pass and/or dynamic filtering        Excessive cordless telephone RF carrier dropout        
Currently used standard acoustic tests frequently produce results that do not adequately correlate to the human perception of a telephone's sound quality. For instance, the measured audio frequency response of a telephone unit A can fail to meet specified limits and yet be ranked much higher by a typical user than a telephone unit B whose measured audio frequency response complies with the specified limits.
The present invention is directed to an improved method and apparatus intended to determine the subjective sound quality of a telephone unit.